Choose a robot mower’s cutting height by matching your grass’s target height to the machine’s actual adjustment range. The highest grass it can enter is a different limit from the height it leaves behind. A dial number is also not necessarily a measurement in centimeters or inches.
Reviewed September 28, 2026. This guide uses manufacturer documentation and university turf guidance. We have not measured these mowers’ cut quality; examples below are calculations and planning tools.
Three heights to check before changing a setting
| Measurement | Meaning | Where to find it |
|---|---|---|
| Target lawn height | The height you intend to maintain for your grass and conditions. | Guidance for the grass species and your region. |
| Mower’s cutting range | The minimum and maximum setting the machine can provide. | Exact model specification and manual. |
| Maximum starting grass height | The grass height permitted before beginning or resuming mowing. | Installation and operation instructions. |
For example, the UK Automower 310 Mark II specification lists a manually adjusted cutting range of 20–50 mm. Husqvarna’s height guidance separately lists 100 mm as the maximum starting grass height for that model group. That does not mean the mower can be set to leave a 100 mm lawn.
Check grass requirements before buying
The University of Minnesota Extension recommends maintaining a typical residential Midwest lawn at 3 inches or more, referring to the cool-season grasses common in that region. It also recommends removing no more than one-third of the leaf tissue in a mowing. This is regional lawn guidance, not a universal height for every grass. See mowing practices for healthy lawns.
Three inches equals 76.2 mm. A mower capped at 50 mm cannot maintain that target, regardless of its app settings or area capacity. If your turf advice calls for a height outside a model’s range, resolve that mismatch before purchase. For a different grass or climate, obtain the corresponding local recommendation.
Record the target and model range in your mower buying checklist. Do not assume a similarly named high-cut variant has the same deck or adjustment range.
Use the one-third rule as a calculation, not a mower limit
To remove no more than one-third of the current grass height, the remaining height must be at least two-thirds of that starting height:
Minimum remaining height = current grass height × 2 ÷ 3.
Hypothetical example: reducing 90 mm grass to 60 mm removes one-third. Reducing the same grass immediately to 40 mm removes about 56%. The second change is much more severe even if a mower has a 40 mm setting.
This calculation does not authorize a robot to enter 90 mm grass. Its starting-height limit, available settings and the condition of the lawn still apply. If the permitted starting height is exceeded, prepare the lawn with suitable equipment before resuming the robot, rather than expecting repeated stalled passes to solve the problem.
Set the height using the method your model actually has
Husqvarna’s adjustment guide separates manual models from electronically adjusted models and area-specific settings. It recommends starting at maximum height for the first few weeks of a new installation, then reducing gradually, helping protect new boundary wire. Apply that brand guidance only where it matches your manual.
- Identify the setting. Record the current dial position or app value, and check its meaning in the manual. “Level 4” is not enough information to infer 40 mm.
- Check the starting grass. Measure representative patches, including the longest section, and compare them with the operation instructions.
- Make an allowed adjustment. Follow the mower’s stop and isolation procedure before touching a manual mechanism. Use the documented control for powered adjustment; do not force the deck.
- Observe the affected area. Record the setting, date and lawn condition. Compare after the mower has actually covered that area, rather than changing several settings in succession.
Use the pattern of an uneven cut to choose the next check
| What you observe | Useful next check | What the observation cannot prove |
|---|---|---|
| The whole lawn is consistently shorter than intended | Compare target height, units and actual selected setting. | That the height motor is faulty. |
| Scalping at one mound or edge | Inspect that location and wheel path with the mower off. | That lowering the whole lawn will fix it. |
| Ragged grass tips or vibration | Inspect the cutting parts according to the manual. | That the displayed height is incorrect. |
| An entire zone remains long | Check whether the mower visited it and whether a separate zone setting applies. | That the mower needs a lower global setting. |
| Height adjustment is stuck or reports an error | Record the message and follow the model’s troubleshooting procedure. | Which internal component has failed. |
Keep hands away from the blade area until the mower is disabled and all movement has stopped. If adjustment remains blocked, the deck is damaged or a fault returns, obtain service advice instead of opening a sealed height mechanism.
For ragged cutting or a problem that started after maintenance, use the blade replacement guide. If the problem appears only in damp conditions, record that distinction and consult the wet-grass guide. A useful adjustment solves a documented mismatch; repeatedly lowering the setting can hide the original symptom.
Update — September 28, 2026: Separated grass height, cutting range and starting-height limits, with labelled model examples.